This application proposes to elucidate the structural principles behind nuclear hormone receptor/corepressor association. It also proposes to define the structural basis for nuclear hormone receptor coactivator binding to the CREB binding protein/p300 family of nuclear cointegrator proteins. These proteins are critical for regulating cell differentiation, proliferation and cell death. Attenuated levels of these proteins have been observed in tumorigenic cell lines. This work is in collaboration with Dr. R. Evans whose group has already cloned the gene sequences for each of the proteins and has additionally identified appropriate peptide/protein domains from each protein component that will be amenable for NMR studies. This application proposes to isotopically label the individual proteins using bacterial expression systems. These proteins will be utilized for detailed heteronuclear multidimensional NMR experiments. Information derived from these experiments will be utilized for detailed structural and dynamic characterizations of the protein/protein complexes. Like many of the nuclear protein binding motifs that have been elucidated so far, the motifs unveiled here will likely represent universal themes for nuclear receptor/corepressor and coactivator/cointegrator associations.